Structural Insights into the Down-regulation of Overexpressed p185her2/neu Protein of Transformed Cells by the Antibody chA21

• Published in: The Journal of biological chemistry Vol. 286; no. 36; pp. 31676 - 31683
• Main Authors: Zhou, Huihao, Zha, Zhao, Liu, Yang, Zhang, Hongtao, Zhu, Juanjuan, Hu, Siyi, Shen, Guodong, Cheng, Liansheng, Niu, Liwen, Greene, Mark I., Teng, Maikun, Liu, Jing
• Format: Journal Article
• Language: English
• Published: 9650 Rockville Pike, Bethesda, MD 20814, U.S.A Elsevier Inc 09.09.2011; American Society for Biochemistry and Molecular Biology
• Subjects: Antibodies; chA21; Cross-link; Crystal Structure; ErbB; Protein Structure and Folding; Protein-Protein Interactions; Receptor Endocytosis; Tumor Therapy; Crystal Structure; Tumor Therapy; Antibodies; chA21; Receptor Endocytosis; ErbB; Cross-link; Protein-Protein Interactions
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M111.235184

p185her2/neu belongs to the ErbB receptor tyrosine kinase family, which has been associated with human breast, ovarian, and lung cancers. Targeted therapies employing ectodomain-specific p185her2/neu monoclonal antibodies (mAbs) have demonstrated clinical efficacy for breast cancer. Our previous studies have shown that p185her2/neu mAbs are able to disable the kinase activity of homomeric and heteromeric kinase complexes and induce the conversion of the malignant to normal phenotype. We previously developed a chimeric antibody chA21 that specifically inhibits the growth of p185her2/neu-overexpressing cancer cells in vitro and in vivo. Herein, we report the crystal structure of the single-chain Fv of chA21 in complex with an N-terminal fragment of p185her2/neu, which reveals that chA21 binds a region opposite to the dimerization interface, indicating that chA21 does not directly disrupt the dimerization. In contrast, the bivalent chA21 leads to internalization and down-regulation of p185her2/neu. We propose a structure-based model in which chA21 cross-links two p185her2/neu molecules on separate homo- or heterodimers to form a large oligomer in the cell membrane. This model reveals a mechanism for mAbs to drive the receptors into the internalization/degradation path from the inactive hypophosphorylated tetramers formed dynamically by active dimers during a “physiologic process.”